Method of operating compression ignition engine



Aug. 24, 1965 AVAILABLE BRAKE HORSEPOWER w. G. LOVELL 3,202,141

METHOD OF OPERATING COMPRESSION IGNITION ENGINE Original Filed Oct. 27.1961 A. Full Diesel B. Natural Gas Plus Tetramethylleud C. Propane PlusTefromethylleud D. Propane Plus Tetroefhylleod LEAD, GRAMS PER THERM OFPRIMARY FUEL INVENTOR.

3,202,141 METHOD OF OPERATING COMPRESSION IGNITION ENGINE Wheeler G.Lovell, Bloomfield, Mich, assignor to Ethyl Corporation, New York, N.Y.,a corporation of Virginia Continuation of application Ser. No. 148,277,Oct. 27, 1961. This application July 1, 1963, Ser. No. 295,585

6 Claims. (Cl. 123-1) This application is a continuation of applicationserial No. 148,277, filed October 27, 1961, which, in turn, is acontinuation-impart of pending applications Serial Numbers 11,416 and11,417, both filed February 29, 1960, all of which are abandoned.

This invention relates to a method of operating an internal combustionengine. More particularly, the invention relates to an efficient andeconomical operation of diesel engines adapted to operate on a dual fuelcycle.

For the purpose of this invention, dual fuel engines are defined ascompression ignition engines which use as a portion of the fuel supply,a normally gaseous material (hereinafter also referred to as the primaryfuel) such as natural gas, liquefied petroleum gas, methane, ethane,propane, etc. Ignition of the gaseous primary fuel is accomplished bythe injection of a charge of diesel fuel (hereinafter also referred toas pilot charge) into the com pressed gas mixture. Thus, normal dualfuel operation comprises induction of a primary fuel-air mixture intothe combustion chamber, compressing this mixture by means of thecompression stroke, and at some point during the compression stroke,injecting a pilot charge of diesel fuel into the compressed primaryfuel-air mixture.

The pilot charge of diesel fuel is injected through a conventionaldiesel fuel injection system and acts as a source of ignition for thecompressed fuel-air mixture. In normal dual fuel operation, air to theengine is not throttled but is constant. Power output from the engine iscontrolled by varying the amount of gaseous fuel admitted into thecombustion chamber. For a given engine, the quantity of the pilot chargeof diesel fuel per cycle is usually fixed, regardless of engine output.At full load the amount of the pilot charge usually represents less than10 percent of the total fuel to the engine.

One of the main incentives for using a dual fuel cycle is economy. Manywidely available gaseous fuels are much cheaper than conventional dieselfuel. Moreover, using gaseous fuels allows smoother, cleaner combustionwith a minimum of combustion chamber deposits. Engine maintenance costsare reduced and engine life is prolonged.

In many instances operating a compression ignition engine on the dualfuel cycle results in a severe penalty, for only a fraction of maximumpower is available as compared with operating the engine as a "fulldiesel. The sharp reduction in power output is due to a loss ofcombustion control. evidenced by rough operation, audible noises,combustion knock, etc. This is very objectionable for it results Thisloss of combustion control is United States Patent 3,202J4l PatentedAug. 24, 1965 in shock loading of pistons, bearings, and other engineparts as well as loss in power output. To avoid this loss of combustioncontrol, engine manufacturers have had to limit the power output of theengine. This is accomplished by reducing the amount of primary fuelintroduced into the combustion chamber during each cycle which in turnresults in lower power output.

The fact that the use of. certain gaseous fuels in a dual fuel operationresults in loss of combustion control has long been recognized. As farback as 1898, Rudolph Diesel recognized this problem. i In his BritishPatent No. 7,657 claiming the method of operating an internal combustionengine on a dual fuel cycle, he stated that he could use illuminatinggas however only in small proportion to the air. In other words theamount of fuel had to be reduced or limited to retain combustioncontrol. Thus, for a period of over 60 years, this problem of loss ofcombustion control when using a dual fuel cycle has plagued theindustry. The problem has not been solved but only circumvented byaccepting the penalty of lems associated with combustion control loss.

It is an object of this invention to provide a method of operating a.dual fuel engine in an economical and efficient manner. Another objectis to provide a method whereby the power output available from a dualfuel engine is equal to or greater than the maximum power available whenoperating under full diesel conditions.

It has now been found that surprisingly, a material normally used as anantiknock agent in gasoline fuels for spark-ignited engines can be usedas a combustion control improver in compression ignition enginesoperated on a dual fuel cycle. Accordingly, the objects of thisinvention are accomplished by the method of this invention which methodcomprises the steps of:

(1) Introducing into the combustion chamber of a compression ignitionengine a gaseous fuel, an organometallic combustion control additive,and air to forma combustible mixture, said combustion control additivebeing present in an amount such that the metal is present in aconcentration of from 0.001 to about 0.5 weight percent based on theweight of said gaseous fuel,

(2) Compressing said mixture to about from to about of its originalvolume so as to be at ateinpera pilot charge optionally containing fromabout 0.001 to about 1 percent of combustion control additive.

The combustion control additives of this invention comprise compoundsselected from the group consisting of organo-lead compounds and ahydrocarbon soluble organometalliccompound of a metal of atomic numberThe above-enumerated combustion control additives 2548 inclusive. 1

may be added singly or in any combination to the gaseous primaryfuel-air mixture. In some situations, it is also desirable to add acombustion control additive to the diesel pilot charge. In any event, inthe practice of this invention, a combustion control additive asdescribed above must be present in the gaseous primary fuel-air mixture.In a preferred method, a relatively volatile additive is added to thegaseous primary fuel and a second, heavier additive which may produce asynergistic effect is added to the diesel pilot charge. A specificexample is to add tetrarnethyllead to the primary fuel andmethylcyclopentadienyl manganese tricarbonyl to the pilot charge.

The inclusion of a material normally used as an antiknock material inthe gaseous primaryfuel permits much greater power to be developed thanheretofore possible. By the use of the method of this invention,combustion control is retained, allowing operation of the dual fuelengine in a manner so as to obtain as much and oftentimes more powerthan that possible when operating the engine as a full diesel. This issurprising for the art has long recognized that organometallic antiknockmaterials such as tetramethyllead, although useful in gasoline fuelsused for spark-ignited engines, were not useful but in some respectseven harmful when included in diesel fuel. In order to understand theimport of this statement, it is necessary to consider the dieselcombustion process.

In diesel operation combustion control is mainly obtained by the rate atwhich diesel fuel is injected into hot, compressed air. The fuelparticles, upon contact with the high-temperature air Within thecombustion chamber, do not ignite instantaneously but there is a delayperiod of several thousandths of a second between the start of fuelinjection and the time that the fuel particles are ignited. Burning thenproceeds in a manner determined by the rate and the total quantity offuel injected into the air charge. Under proper conditions, the burningproduces a smooth, even pressure rise in the combustion chamber. Theignition delay period is critical, for if the fuel does not ignitewithin the proper interval, too large an amount of fuel will have beenmixed with the air charge. When ignition does take place, the largeramount of fuel will burn in a relatively short time, resulting in anabnormal, high rate of pressure rise. A long ignition delay period alsoallows time for pre-fiame reactions to take place in the fuel-airmixture before ignition occurs and the reactions result in productswhich burn with extreme rapidity, further contributing to the excessive,rapid pressure rise. The rate of pressure rise may become so rapid thatrough engine operation, evidenced by loss of power, combustion knock,etc. will occur. Also with a cold engine and with low intake airtemperatures, too long a delay period produces misfiring and uneven orincomplete combustion with consequent smoke and loss of power.

With a proper ignition delay period, ignition occurs before thepro-flame reactions have proceeded and when the proper amount of fuelhas been injected into the air charge, producing a smooth, gradualpressure rise.

The ignition delay period is associated with the chemical composition ofthe fuel. Ignition delay characteristics are so important that dieselfuel specifications almost universally include an ignition delaycharacteristic. In an engine test procedure under ASTM Designation D-6l3-48T, the ignition delay characteristics of the diesel fuel arecompared with those of two pure hydrocarbon reference fuels, cetane anda-methylnaphthalene. Cetane has a very high ignition quality (shortignition delay period) and, accordingly, is designated at the top of thescale with a cetane number of 100. wMethylnaphthalene has an exceedinglylow ignition quality (long ignition delay period) and represents thebottom of the scale with a cetane number of Zero. Blends of these twohydrocarbons A. with those of the blend and a cetane number isaccordingly assigned to the diesel fuel.

With spark-ignited internal combustion engines, the primary fuelcharacteristic is octane number. This is the measure of the ability of afuel to resist pre-spark or uncontrolled and erratic combustion. As withdiesel fuel, the end objective is to control combustion so as to obtaina smooth, even pressure rise. The term designating this quality is knownas octane number. The resistance of the fuel to pre-flame combustion,uncontrolled combustion, etc. usually known as knock, is compared withthat of isooctane, the top of the scale, and n-hcptane, the bottom ofthe scale. A single-cylinder engine is operated in accordance with thestandard ASTM procedure and the antiknock quality of the fuel is matchedwith that of a blend of isooctane and heptane. The percentage ofisooctane in the blend having the same antiknock properties as those ofthe fuel is assigned as the fuel octane number. The higher the octanenumber the more desirable the fuel.

Thus, with normal diesel fuel operation, in order to retain combustioncontrol, the desirable fuel quality is ability to ignite within a fairlyshort time, whereas with spark-ignited engines the desirable fuelquality is ability to resist combustion until ignited by the spark. Fromthese considerations it would be expected, and the art recognizes, thata good diesel fuel would make apoor fuel for spark-ignited engines andvice-versa. This is verified from the literature. Knock Characteristicsof Hydrocarbons, by W. G.'Lovell, published in Industrial andEngineering Chemistry, vol. 40, No. 12, December 1948, presents researchoctane numbers for a variety of pure hydrocarbons. CombustionCharacteristics of Compression Ignition Engine Fuel Components, by D. R.Olsen et al., presented at the SAE National Fuels and Lubricantsmeeting, November 2, 1960, Tulsa, Oklahoma, reports cetane numbers forvarious hydrocarbons. Cetane numbers and octane numbers forpurehydrocarbons common to both of the aforementioned papers arepresented in Table I.

1 Cetanenumbers were determined for the indicated hydrocarbon in a.concentration of 20 percent in a base fuel composed of 25 percentn-cetane and percent isooctane. The base fuel ha ad cetane number of 38.

The data of the above table clearly demonstrate that fuels most suitedfor diesel operation are the least desirable for spark ignitionoperation. Heptane, which has the highest cetane number of the materialsshown, has the lowest octane number. Conversely, toluene, which has thelowest cetane number, has an exceedingly high octane number. V

The effect of including organometallic antiknock compounds in dieselfuels is shown in Table II. Methylcyclopentadienyl manganese tricarbonyland tetraethyllead (TEL), materials used in commercial fuels for sparkignition engines, were added to several different diesel fuels and thecetane number was determined in accordance with. ASTM Test DesignationD-613-48T..

TABLE II Efiect of organometallic antiknock compounds on diesel fuelcetane number Cetzne Number Mn, gun/gal. as methylcyclopentadienylmanganese trlcarbonyl Thus, methylcyclopentadienyl manganese tricarbonyland tetraethyllead, although widely used to improve the combustionproperties of gasoline, have an opposite and adverse effect on cetanenumber of diesel fuel.

The data of Tables I and II thus amply demonstrate what is well known tothose skilled in the art.that spark ignition engines and compressionignition engines are opposites; that cetane numbers and octane numbersbear an inverse relationship; and that the most desirable fuels forefiicient operation of spark-ignited engines are the least desirable foreflicient operation of diesel engines. This is true whether the cetanenumbers and octane numbers are due to the inherent properties of thehydrocarbon constituents or due to the addition of chemical additives.In other words, it has been Well known that those hydrocarbon componentsand chemical additives which produce a beneficial effect ingasoline-type fuels produce an adverse affect with respect to combustioncontrol when included in diesel fuels. Contrary to the teachings of theprior art, it has now been discovered that materials normally used forantiknock purposes in gasoline can be used as combustion controlimprovers to markedly increase the power output of a compressionignition engine operated on a dual fuel cycle. In short, contrary toprior art teachings, primary fuels of lower cetane numbers are desirablefor maximum power output of a dual fuel com pression ignition engine.

Among the combustion control improvers usable in the method of thisinvention are lead alkyls wherein each alkyl group contains up to about6 carbon atoms and includes compounds such as tetramethyllead,tetraethyllead, tetraisopropyllead, tetrapropyllead, tetrabutyllead,tetraamyllead, tetraoctyllead, dimethyldiethyllead, hexyltriethylleadmethyltriethyllead and the like. The phenyl and mixed phenylalkylcompounds such as tetraphenyl, trimethylphenyl, diphenyldiethyl,triphenylpropyl, etc. are also useable.

Also included within the scope of the combustion control improvers ofthis invention are organic compounds of a metal having an atomic numberof from 25-28, said compounds characterized by being covalent, bypossessing in addition to the said metal only elements selected from theclass consisting of carbon, oxygen, hydrogen and nitrogen, by containingat least one group selected from the class consisting ofcyclopentadienyl groups and the carbonyl group, and by containing from 5to carbon atoms in the molecule. The metals of atomic numbers 28 aremanganese, iron, cobalt and nickel.

The preferred manganese compounds are the cyclo pentadienyl manganesetricarbonyls as described for ex- 6 ample in US. Patents 2,818,416 and2,818,417. Illustrative of these compounds are cyclopentadienylmanganese tricarbonyl; methylcyclopentadienyl manganese tricarbonyl;indenyl manganese tricarbonyl; manganese pentacarbonyl; and so on.

The preferred nickel compounds are of the type as described in US.Patent 2,818,416. These include cyclopentadienyl nickel nitrosyl;methylcyclopentadienyl nickel nitrosyl; indenyl nickel nitrosyl and thelike.

The preferred iron compounds of this invention are thedi-cyclopentadienyl iron compounds; e.g., bis-cyclopen-ta dienyl iron;bis-methylcyclopentadienyl iron; bis-butylcyclopentadienyl iron. Othercompounds such as iron pentacarbonyl and butadiene iron tricarbonyl arealso effective.

The preferred cobalt compounds include the cobalt carbonyls such ascobalt tetracarbonyl; cyclopentadienyl cobalt dicarbonyl;1-pentyne-cohalt tetracarbonyl and co balt pentacarbonyl mixedcomplexes.

'The preferred concentration range for the combustion control improversis from about 0.03 to about 0.25 percent metal based on the weight ofthe primary gaseous fuel. At these concentrations the additives areextremely effective on a cost-effectiveness basis. When also included inthe diesel fuel pilot charge, the preferred metal concentration is fromabout 0.05 to about 0.4 weight percent of the diesel fuel.

. The most preferred organometallic compound is tetramethyllead. Thismaterial is extremely effective in increasing the maximum power outputof a dual fuel engine and furthermore is the most volatile and thus morecompatible with the gaseous fuels than are any of the aforementionedheavier organometallic compounds. With certain fuels synergistic effectscan be obtained using a combination of tetramethyllead and a heavier,second organometallic compound such as methylcyclopentadienyl manganesetricarbonyl. In such cases the second organometallic compound ispreferably included in the diesel fuel pilot charge.

Another advantage in using tetramethyllead is that because of its highvolatility, it can be more easily carried into the combustion chamberwith the gaseous fuels. With one system to handle, deliver, and meter aliquefied petroleum gas-additive mixture to the engine, the liquid LPGin which additive is dissolved is stored in a suitable container. Due toits own pressure the liquid is forced into a combination vaporizer andpressure regulator and there heated with engine coolant. The liquid isflashed and vaporized at a pressure slightly above atmospheric. Thegaseous material is then metered and introduced into the combustionchamber. In such a system, if the com bustion control additive is not ofsufiicient volatility, it will remain in the vaporizer as a' liquid.Aside from the obvious disadvantage of not having the material reach thecombustion chamber, maintenance and clean-up problems are posed. With amaterial such as tetramethyllead, tests have shown that the liquidtemperature before flashing can be as low as 60 F. and still haveessentially percent vaporization of the tetramethyllead. Moreover,substantial vaporization of tetramethyllead takes place at temperatureswell below, 60 F. The compati bility of tetramethyllead with gaseousfuels is surprising in view of the wide differences between itsvolatility and that of the gaseous fuel. This is one additional featurewhich makes tetramethyllead extremely well suited as an additive togaseous fuels.

The gaseous primary fuels useable in the method of this inventionbroadly include any material which is normally gaseous at ambientpressure and temperature and which is capable of being ignited in aninternal combustion engine. This includes materials such as natural gas,well head gas, sewer gas, coal gas, water gas, producer gas, coke ovenor blast furnace gas, liquefied petroleum gases and hydrocarbon gases.The preferred primary fuels are hydrocarbons containing from one to 4carbon propylene, butane, butylene, and mixtures thereof.

atoms including methane, ethane, ethylene, propane, A specific mixtureof these light hydrocarbon gases, known as liquefied petroleum gas (LPG)is also preferred. L.P.G. is mainly liquid propane, propylene, butane ormixtures thereof, sometimes containing trace quantities of ethane,isobutane, pentane and/or isopentane.

The primary fuel may also contain other additives. Typical of these areantioxidants, (e.g. N, N'-di-sec-butylp-phenylene diamine;p-N-butylaminophenol; 4-methyl-2, 6-di-tert-butylphenol;2,6-di-tert-butylphenol); metal deactivators (N,N disalicylidene 1,2diaminopropane, etc.); dyes; phosphorus additives (e.g.tri-[i-chloropropyl thionophosphate; dimethyltolyl phosphate;dimethylxylyl phosphate; phenyldimethylphosphate; tricresyl phosphate;trimethylphosphate, etc.); halohydrocarbon scavenging agents such asethylene dibromide, ethylene dichloride, methyl bromide, methylchloride, etc.

The diesel fuel base stocks used for the pilot injection fuel pursuantto the invention can be derived from a wide variety of crude sources.Furthermore, the diesel fuel may be made up of straight run dieselfuels, catalytically cracked stocks, No. 2 burner oils, light residualstocks and the like. These diesel fuels fall within the boiling range offrom about 300 to 725 F., with intermediate fractions boiling attemperatures between these limits. The initial and final boiling pointsof the diesel fuels may vary to some extent from the above limitsdepending upon the grade of diesel fuel, its source, and its method ofmanufacture and formulation. Generally, any of the commercial-typeavailable diesel fuels may be used as the pilot charge in the method ofthis invention. The cetane number may vary from about 30 to 65. In orderto insure proper ignition, it is desirable that the diesel fuel have acetane number of at least about 40.

The diesel fuels may also contain other additives such as stabilizers;stability-compatibility agents; cetane improvers such as alkyl nitrates(amyl nitrate); phosphate esters; corrosion inhibitors; metaldeactivators; dyes; and the like. Amounts of these additives in therange of from about 0.001 to about 2 percent based on the weight of thediesel fuel are usually effective.

The relative amounts of diesel fuel pilot charge and primary fuel canvary over wide limits. A minimum amount of the diesel pilot charge willbe required to provide continuous :and efficient ignition of the totalcharge. This amount is usually at least 1 percent of the total fuel.While the pilot charge can be increased to about 50 percent or more ofthe total fuel, to obtain the maximum benefits of this invention thepilot charge should be less than 50 percent. A preferred range for thediesel pilot charge is from about 2 to about 10 percent of the totalfuel charge at full load.

The fuel-air ratios for the practice of this invention are subject towide variations. In the compression ignition cycle, air is not throttledbut is set at a somewhat constant rate. Since power output is controlledby throttling the fuel, air-fuel ratios vary with power demand. Underidling conditions air-fuel ratio may be as high as 100:1, while underfull load conditions the mixture may be considerably enriched so as tohave air-fuel ratios as low as about 13:1. The optimum air-fuel ratiosunder full load are of the order of from about 17:1 to 14:1.

The compression ratios of the engines must be high enough to raise thetemperature of the compressed air to a level so as to ignite the dieselfuel pilot charge. Thus the compression ratio should be at least about12:1. Higher compression ratios may be used but at ratios higher thanabout 22:1 additional problems are presented. The engine must bedesigned so as to withstand extremely high temperatures and pressures,and the diesel fuel injection system must be capable of injection atthese high pressures.

This invention is applicable to two-cycle and four-cycle diesel engineoperation. In the two-cycle engine, the

'8 gaseous fuel is introduced into the combustion chamber after thescavenging operation has been completed. In other words, the gaseousfuel is introduced after the piston has covered the intake ports on itsupward stroke and the exhaust valves (or exhaust ports) have beenclosed. During and after this introduction, the piston continues itsupward stroke thereby compressing the airgaseous fuel mixture.

At some point, usually before top dead center, the

.pilot injection of the diesel fuel is made and compression ignitioninitiated. In four-cycle engine operation,

.the gaseous fuel can be supplied to the air intake manifoldor it can beintroduced through a valve into the combustion chamber as in the case ofthe two-cycle engine. The method of this invention and the benefitsobtained therefrom are illustrated by the following examples.

EXAMPLE 1 A Hercules diesel model DD-169-H; 16.221 compression ratio,four-cycle, 169 cubic inch direct injection en gine was used in thesetests. The engine was equipped with a Bosch variable injection timingfuel system. The engine was converted so as to be operable both as afull diesel and also on a dual fuel cycle. Provisions were made to allowthe use of either L.P.G.-type fuels or natural gas as the primary fuel.

Provisions were made to detect loss of combustion control by use of aKistler Model 601 pressure transducer in one cylinder of the engine. Thesame transducer was used for pressure-time trace display on a dualbearnoscilloscope. The engine was coupled to a DC. dyna mometer and airconsumption was measured by a smooth approach orifice head of a surgetank.

Engine speed was maintained at 1600 r.p.m., intake air temperature wasambient in the dynamometer room, and engine jacket temperature wascontrolled to 170 F. The engine was operated as a full diesel and alsousing a dual fuel cycle. Under a dual fuel operation, the amount of thediesel pilot charge was maintained constant about 1.65 lbs. of fuel perhour. Propane-and natural gas containing and void of organometalliccompounds were used as primary fucls. The obtainable brake horsepower,as limited by loss of combustion control, was measured.

The organometallic additive concentration in some instances will beexpressed as grams of metal additive per t-herm (100,000 B.t.u.) offuel. The use of this term is convenient for it provides a directcomparison of additive effectiveness in liquid and gaseous fuels andtakes into account differences in heating value between certain gaseousand liquid fuels when compared on a volume basis. For orientation, onegram per gallon in propane is equal to about 1.2 grams per therm. Lowerheating values were used for calculations. The heating value-massrelationship for the fuels is diesel fuel 18,450 B.t.u./lb.; propane19,800 B.t.u./lb.; and natural gas 18,500 B.t.u./lb.

The propane used was technical grade with a minimum purity of percentpropane. The natural gas was composed of about 87 percent methane, 3.4percent ethane, 7 percent nitrogen, 1 percent propane and trace amountsof butanes, pentanes, hexanes, carbon dioxide and helium. The dieselfuel used had an API gravity of 36.4 and a cetane number of 49.6.

The engine, when operated as a full diesel according to themanufacturers specification, developed 34 horsepower at a diesel fuelconsumption rate of 13.3 lbs/hour.

The engine was then operated on a dual fuel cycle using various primaryfuel flow rates and a constant diesel pilot charge fuel rate of about1.65. The quantity of the primary fuel metered into the combustionchamber was increased until combustion control was lost. This wasevidenced by high frequency vibrations on the pressure-time trace or ona dp/dt trace on an oscillocompound per therm of primary fuel scopescreen. It was also possible to detect combustion knock audibly. Thehorsepower developed for various operating conditions is shown in FIGURE1.

In the figure, the brake horsepower obtained with various primary fuelsat the point where the engine was limited by loss of combustion controlis plotted as the ordinate versus concentrations of organometalliccompounds as the abscissa. The point A represents the availablehorsepower when operating as a full diesel according to themanufacturers specifications. Curves B, C, and D show the availablepower when operating on a dual fuel cycle. Curve B shows the results ofusing natural gas containing various concentrations of tetramethylleadas the primary fuel. Curves C and D show the results of using propanecontaining various concentrations of tetramethyllead and tetraethyllead,respectively.

As shown by the figure, using unleaded natural gas as the primary fuelresulted in a power output essentially equalto full diesel operation.However, using propane the enginedeveloped only 23 horsepower before itbecame knock limited. This represents only 68 percent of the powerobtainable when the engine is operated as a full diesel.

By the addition of tetraethyllead or tetramethyllead to the primaryfuel, combustion control was retained and much higher fuel rates andhence markedly increased power output were obtainable. The outstandingbenefits obtained due to the addition of 3.5 grams of alkyllead areshown in the following table.

1 Pb added as tetramethyllead. 2 Pb added as tetraethyllead.

NorE.Bralre horsepower with full diesel operation equals 34.

The data of FIGURE I and Table III demonstrate that the organometalliccompounds of this invention are very effective in increasing theallowable .power of a compression ignition engine operated on a dualfuel cycle. When the engine .is operated on a dual fuel cycle usingunleaded propane as the primary fuel, only a fraction of the power isavailable as compared to operat- Since propane is the major coning as afull diesel. stituent of L.P.G., a severe power penalty has heretoforebeen associated with the use of this material in a dual fuelapplication. However, by the use of the method of this invention it isnow possible to use this widely available and relatively economicalhydrocarbon in a dual fuel application without any loss in the availablepower. In fact at a moderate tetraalkyllead concentration, a dual fuelengine can be operated so as to develop more power than available understraight diesel operation. Thus,

operating the engine as a full diesel, as recommendedby themanufacturer, 34 horsepower was developed. Using unleaded propane as theprimary fuel in a dual fuel cycle, the engine developed 23horsepower-only 68 percent of that available as a straight diesel.However, the addition of 3.5 grams of lead per therm of propanepermitted the engine to develop more power than available whenoperatingas a full diesel. The use of tetra 7 l6 methyllead, the mostpreferred additive of this invention, resulted in a 58 percent powergain over that obtainable when using unleaded propane as the primaryfuel. This value also represents a 6.8 percent power gain over thatobtainable when operating as a straight diesel.

The use of small amounts of tetramethyllead in natural gas permittedmore power to be developed using the dual fuel cycle than obtainablewith full diesel operation. At a higher tetramethyllead concentration of4.5 grams of lead per therm of natural gas, the engine operating on adual fuel cycle, developed 43.2 brake horsepower without loss ofcombustion control. This represents a 24 percent improvement over the 34horsepower obtainable when operating as a full diesel, and a 25 percentimprove ment as compared to dual fuel operation using unleaded naturalgas. Thus by the use of the method of this invention not only can acheaper fuel be used, but the available engine power is markedlyimproved.

As shown in the above Table III, propane containing tetramethylleadallows greater power to be developed than the same fuel containingtetraethyllead. Another advantage in using tetramethyllead is thatbecause of its high volatility it is more easily vaporized into, andmore compatible with, the gaseous fuel. For these reasons the use oftetramethyllead in the primary fuel in a dual fuel operation constitutesa most preferred embodiment of this invention.

EXAMPLE II TABLE IV Increase in brake horsepower due to tetraalkylleadPercent Grams Pb/ Brake Increase Fuel therm of horseover propane powerunleaded 40 Wt. percent natural gas 60 Wgj percent propane.

Do 60 Wt percent natural gas 40 Wt];) percent propane.

NOTE.Brake horsepower with full diesel operation equals. 34.

The data of Table IV, consistent with those of the previous example,show that by using a moderate amount of a tetraalkyllead compound,mixtures of propane and natural gas can be effectively used in a dualfuel cycle without sacrifice in available power. In fact, increasing.the concentration of the tetraalkyllead compound allows- A dual fuelengine was operated in accordance with. the procedure of Example I. Apilot fuel injection rate it of 1.8 pounds of diesel fuel per hour wasused. The

engine was operated on a dual fuel cycle using unleaded 1 1 and leadedpropane as the primary fuel and diesel fuel with and without manganeseas methylcyclopentadienyl manganese tricarbonyl in the pilot charge. Forthe various fuel-additive combinations, the power output as limited byloss of combustion control was determined and is shown in Table V.

TABLE V Efiect of including a combustion control additive in both theprimary fuel and diesel pilot charge Power increase due to combustioncontrol Grams of Pb/ Grams of Mn] Available additive gal. of primarygal. of diesel brake fuel pilot charge 2 horsepower Horsc- Percent power1 Pb added as tetramethyllead. 2 Mn added as methylcyclopentadienylmanganese tncarbonyl.

As shown by the above data, available power can be increased byincluding a combustion control additive to either the primary fuel orthe pilot diesel charge. However, much more eflicient results areobtained by including the additive in the primary fuel charge. As shownin the above table, when 6.0 grams of manganese were added to the pilotcharge, power was improved by about 13 percent. This amount of manganeseis roughly equivalent to just over 1 gram of metal per gallon of primaryfuel. As shown in the table, 1.05 grams of lead added to the primaryfuel increased horsepower by about 35 percent; Thus in the eflicientutilization of the method of this invention, a combustion controladditive must be included in the primary charge.

The above data demonstrate that synergistic effects can be obtained byincluding an alkyllead compound in the primary gaseous fuel and adding amanganese compound to the pilot charge. The benefits thus obtained aregreater than the sum of the improvements due to using manganese solelyin the pilot charge and using the alkyllead solely in the primary fuel.For example, using 6 grams of manganese per gallon of pilot chargeincreased the available power by 2.9 horsepower, whereas using 3.15grams of lead per gallon of primary fuel increased power by 9.6horsepower.

additives in the respective fuels concurrently would increase power by12.5 horsepower, the sum of their individual effects. However, as shown,power was actually increased by 14.7 horsepowerabout 18 percent moreimprovement than would have been expected.

EXAMPLE IV The compression ignition engine is operated in accordancewith the procedure of Example I using commercial liquefied petroleum gas(L.P.G.) as the primary fuel and a commercial diesel fuel having acetane number of 40 as the pilot charge. The L.P.G. is composed of 53per cent propylene, and 46 percent propane, the remainder beingessentially trace amounts of ethane, butane and pentane. Operating on adual fuel cycle, the available power, as limited by loss of combustioncontrol, is only a fraction of that obtainable when operating as a fulldiesel. The engine is then operated on a dual fuel cycle using L.P.G. towhich has been added 2.8 grams of lead per gallon as tetramethyllead.Under full load conditions, the pilot charge rate is such that theweight ratio of .diesel fuel pilot charge to gaseous primary fuel is0.015 :1. The available power under these conditions is markedlyincreased and is essentially equal to that obtained when operating as afull diesel.

EXAMPLE V The procedure of Example IV is repeated but combustion controladditives are added to both the primary fuel and to the diesel pilotcharge. Thus operating on a dual fuel cycle using L.P.G. 3.0 grams oflead per gallon as the primary fuel, and diesel fuel containing 1.0grams of iron per gallon as dicyclopentadienyl iron, the available poweris greater than that obtained when operating as a full diesel.

EXAMPLE VI The dual fuel engine of Example I is operated using L.P.G.containing 0.5 weight percent lead as tetramethyllead as the primaryfuel and a 45 octane number diesel fuel containing 0.5 weight percentnickel as nickel carbonyl. Under full load conditions, the weight ratioof diesel fuel pilot charge to primary gaseous fuel is about 1:4. Asignificant increase in available power is obtained as compared tooperating the engine on a dual fuel cycle without the use of combustioncontrol additlves.

Further primary fuel and diesel pilot charge fuels are illustrated inthe following examples in Table VI.

Some of the preferred liquefied petroleum gas compositions are shown inthe examples of Table VII. In some instances, the fuels also contain ahalohydrocarbon scavenging agent. A theory of this material is definedas the theoretical amount required to react with all the It would beexpected that using these 55 lead present to form lead halide.

TABLE VI Primary gaseous fuels and diesel pilot charge fuels for dualfuel operation Additive, Wt. Percent Metal in Diesel Fuel ExamplePrimary fuel composition, Vol. percent Primary Fuel Pilot Charge l i esel iil Metal in Octane N 0.

VII 75 Propane, 25 Butane 0.5 as Tetramethyllead 50 0.01 asmcthylcyclopentadicnyl manganese tricarbonyl. VIII 50 Propane, 40Butane, 1O Propylcne 0.04 as cyclopcntadienyl nickel nltrosyL. 0.02 ascyelopentadienyl cobalt dicarbo 1. IX Methane, 20 Ethane, 10 Ethylene0.001 asthDllmgtllilyhiethyllead, 0.001 as 33 0.15 as diciglopcntadienyl iron.

rime y e y ea X 55 Propane 25 Butane 20 Propylene 0.05 as Tetraethyllead0.025 as Dl- 30 0.2 as c clo methyldiethyllead 0.055 asTrirnethyltricarbguyli manganese XI Butane 10 P 1 o zi ii 1gitmilethynead' ropy ene as icyc open a eny iron 42 0.1 a; n XII 30Propane, 30 Propylene, 40 Butanc..- 0.2 as Cobalt carbonyl 48 0.4 niiligil c y zzilgei itadienyl nickel nltrosyl.

TABLE VII Primary fuel compositions Example LP gas comp. volume /0 Lead,gmJgal. Scavenger, theories 50 Propane, 40 Butane, l0 Propylene 75Propane, 25 Butane 50 Propane, 40 Butane, Propylene 55 Propane, 45Butane 25 Propane, 50 Butane, 25 Propylene 60 Butane, 40 Propylene 60Propane, Butane, 20 Propylene 30 Propane, 50 Butane, 20 Propylene 3.0 astetraethyllead.-- 0.l as tetraethyllead. 1.5 as tetraethyllead,

lead. 1.0 as tetraethyllead 0.25 ais tetraethyllead, 0.75 astetramethyl- 0.;5 ais tetraethyllead, 0.25 as tctramethy 1- 1.5 asdtetraethyllead 1.0 as methyltriethyl- 1.0 as tetraethyllead, 2.5 asdimethyldiethyllead. i

2.5 asdtetraethyllead, 2.0 as trimethylethyl- 0.5 as tetraethyllead, 0.5as dimethyldiethyllead, 0.5 as tetramethyllead. 1.5 as tetraethyllead,1.0 as methyltriethyl- 0.5ials methyl bromide, 1.0 as methyl chlo-Propane, 50 Butane, 25 Propylene 3.5 as tetraethyllead 0.5dash lethglenedihromide, 1.0 as ethylene 1c on e. 60 Butane, 40 Propylene... 4.5 astetraethyllead 0.315 alsleth lene dibromide, 1.50 as ethylene ic ori e.90 Butane, 10 Propylene 6.0 as tetraethyllead 0.553s methyl bromide, 1.0as methyl chlo- Il e.

0.53s methyl bromide, 1.0 as methyl chlor1 0. 1.0 as methyl chloride.

0.5 as ethylene dibromide, 1.0 as ethylene dichloride.

0.75 as ethylene dibromide. 1.50 as ethylene dichloride.

1.0 as ethylene dichloride.

0.1 as ethylene dibromide, 0.2 as ethylene lead, 1.5 as tetramethyllead.dichloride. XXVII Propane, 30 Butane, Propylene 2.0 as tetraethyllead.1.5 as trimethylethyl- 1.0 as ethylene dibromide, 1.5 as ethylene lead,1.0 as tetramethyllead. dichloride. XXVIII 60 Propane, 40 Butane 1.0 astetraethyllead, 0.5 as methyltriethyl- 0.5 as methyl bromide, 1.0 asmethyl chlo lead, 0.7 as dimethyldiethyllead. ride. XXIX 55 Propane,Butane 1.0 as tetraethyllead, 0.5 as methyltriethyl- 0.5 as methylbromide, 1.0 as methyl chlolead, 0.7 as dimethyldiethyllead, 1.0 asride. tetramethyllead. XXX Propane, 25 Butane, 20 Propylene 1.0 astetraethyllead, 0.5 as dimethyldi- 0.5 as ethylene dibromldle, 1.5 asethylene ethyllead, 0.5 as trimethylethyllead. 2.0 dichloride.

as tetramethyllead. XXXI 100 Propane 3.0 as tetramethyllead XXXII 70Propane, 30 Butane 3.0 as tetramethyllead A variety of methods areavailable to deliver the combustion control additive into the combustionchamber. The specific technique will vary depending upon the physicalstate of the primary fuel. In the practice of this invention the primaryfuel may be stored in either a liquid or gaseous state. Higher boilingfuels such as mixtures comprising a major portion of propane andcontaining smaller amounts of pentane, butane, ethane, and methane maybe stored under pressure in a liquid state. Lighter hydrocarbons such asnatural gas, ethane, and methane are normally stored under pressure in agaseous state.

When using fuel stored as a liquid such as L.P.G., the antiknockmaterial may be simply added to the fuel in its liquid state. Due to itsown pressure, the liquid fuel is forced from the storage tank into acombination vaporizer and regulator where, along with the combustioncontrol additive, it is vaporized. External heat from the engine coolantmay be used to insure complete vaporization of the fuel-additivemixture. The evaporated mixture, along with air, is then metered intothe manifold and inducted into the combustion chamber by conventionalmeans.

When the primary fuel is stored in the gaseous state, a small amount ofliquid propane or L.P.G. may be used to carry the metal additive intothe intake manifold or directly into the combustion chamber. A mixtureof from about 3 to 90 percent combustion control additive in propane maybe delivered into the vaporizer-regulator section as described above,and the evaporated mixture then mixed with the primary gaseous fuelprior to introduction into the intake manifold. Alternatively, thevaporized additive-propane mixture may be delivered directly into thecombustion chamber and there mixed with the primary fuel.

The carburetor principle commonly used in gasoline engines may also beutilized to introduce the combustion control additive into a gaseousfuel stream. The gaseous primary fuel passes through the venturi portionand the additive is metered in from the float chamber through jets.Still another method is direct injection of the additive into thecombustion chamber similar to that used to inject diesel fuel. Theadditive may be injected in a pure state or diluted in a liquid fuelsuch as L.P.G. or propane. Still another method contemplates the use ofequipment similar to that used in continuous flow manifold injectionsystems used for injection of gasoline into the air supply forautomotive-type fuel injection systems.

The additive may also be carried into the combustion chamber with theair stream. However, since in many two-cycle and supercharged enginesair is used to scavenge the cylinders of residual products, a portion ofthe additive would be lost with the scavenged products. In mostsituations it is preferable to introduce the additive into thecombustion chamber via the primary, gaseous fuel stream.

It is also possible to use more elaborate equipment to meter in only theamount of theadditive required to retain combustion control. Duringstart-up and under low-power requirements, only minor amounts, or insome cases, no additive will be required. At higher power demands whereprimary fuel rate is increased, the concentration of the combustioncontrol additive may be increased so as to retain combustion control.Metering controls to proportion additive flow rate to primary flow atpredetermined ratios may be utilized, or pressure detectors may be usedto increase the amount of the additive when abnormal combustion isapproached.

Methods for the preparation of the foregoing metal compounds haveappeared in the literature. Thus, the preparation of lead alkyls by thealkylation of sodiumlead alloys is described in such patents as U.S.2,635,107. A way of preparing manganese pentacarbonyl is described inUS. Patent 2,822,247. The preparation of the other simple metalliccarbonyls is so well known as to be matters of common knowledge in thechemical arts. References to the preparation of the simplecyclopentadienyl metal compounds are given in Rochow et al., TheChemistry of Organometallic Compounds, John Wiley and Sons, Inc., NewYork, 1957. Preparation of the mixed cyclopentadienyl-carbonylcompounds, including the preferred cyclopcntadienyl manganesetricarbonyls, is described in US. Patents 2,818,416 and 2,818,417. Theolefinically coordinated iron tricarbonyls are made 15 as described byReihlen et al., Annalen der Chemie, vol. 482, pages 161182.

I claim:

1. A method of operating a compression ignition engine which comprisesthe steps of:

(1) introducing into the combustion chamber of a compression ignitionengine a combustible mixture which comprises a gaseous fuel, anorganometallic combustion control additive and air,

(.2) compressing said mixture to from about to about & of its originalvolume so as to raise the temperature of said mixture to a levelsufficient to ignite diesel fuel,

(3) injecting into the combustion chamber a pilot charge of diesel fuelso as to initiate combustion of the total mixture, the weight ratio ofsaid pilot charge to said gaseous fuel being from about 0.01:1 to about1:1;

said organometallic additive being selected from the group consisting oftetraalkyllead compounds containing from one to about 6 carbon atoms ineach alkyl group, and organic compounds of a metal having an atomicnumber of from 25-28, said organic compounds characterized by beinghydrocarbon-soluble, by being covalent, by possessing in addition tosaid metal only elements selected from the group consisting of carbon,oxygen, hydrogen and nitrogen, by containing at least one group selectedfrom the class consisting of cyclopentadienyl groups and the carbonylgroup, and by containing from about to 20 carbon atoms in the molecule;said organometallic additive being present in an amount such that theconcentration of metal of said organometallic additive is from 0.001 toabout 0.5 weight percent based on the' weight of said gaseous fuel.

2. The method of claim 1 wherein said pilot charge of diesel fuel ischaracterized by containing from 0.001 to about 0.5 weight percent ofmetal as said combustion control additive.

3. The method of claim 1 wherein said organometallic combustion controladditive is a tetraalkyllead compound having alkyl groups containing upto about 6 carbon atoms and said pilot charge of diesel fuel beingcharacterized by containing from about 0.001 to about 0.5 weight percentof a metal as a compound selected from the group consisting of organiccompounds of a metal having an atomic number of from 2528, saidcompounds characterized by being hydrocarbon soluble, by being covalent,by possessing in addition to said metal only elements selected from thegroup consisting of carbon, oxygen, hydrogen and nitrogen, by containingat least one group selected from the class consisting ofcyclopentadienyl groups and the carbonyl group and by containing fromabout 5 to 20 carbon atoms in the molecule.

4. The method of claim 1 wherein said organometallic combustion controladditive is tetramethyllead and said pilot charge of diesel fuel ischaracterized by containing from about0.001 to 0.5 weight percent ofmanganese as a cyclopentadienyl manganese tricarbonyl compound.

5. The method of claim 1 wherein said gaseous fuel is propane and saidorganometallic combustion control additive is tetramethyllead, theweight ratio of said gaseous fuel to air under full load conditionsbeing from about 1:14 to 1:17.

6. The method of claim 4 wherein said manganese compound ismethylcyclopentadienyl manganese tricarbonyl.

References Cited by the Examiner UNITED STATES PATENTS 673,160 4/01Diesel l2327 2,818,416 12/57 Brown et al. 1231 2,818,417 12/57 Brown etal. l231 2,965,085 12/60 Kohler l23119 RICHARD B. WILKINSON, PrimaryExaminer.

1. A METHOD OF OPERATING A COMPRESSION IGNITION ENGINE WHICH COMPRISESTHE STEPS OF: (1) INTRODUCING INTO THE COMBUSTION CHAMBER OF ACOMPRESSIN IGNITION ENGINE A COMBUSTIBLE MIXTURE WHICH COMPRISES AGASEOUS FUEL, IN ORGANOMETALLIC COMBUSTION CONTROL ADDITIVE AND AIR, (2)COMPRESSING SAID MIXTURE TO FORM ABOUT 1/12 TO ABOUT 1/22 OF ITSORIGINAL VOLUME SO AS TO RAISE THE TEMPERATURE OF SAID MIXTURE TO ALEVEL SUFFICIENT TO IGNITE DIESEL FUEL, (3) INJECTING INTO THECOMBUSTION CHAMBER A PILOT CHARGE OF DIESEL FUEL SO AS TO INITIATECOMBUSTION OF THE TOTAL MIXTURE, THE WEIGHT RATION OF SAID PILOT CHARGETO SAID GASEOUS FUEL BEING FROM ABOUT 0.01:1 TO ABOUT 1:1; SAIDORGANOMETALLIC ADDITIVE BEING SELECTED FROM THE GROUP CONSISTING OFTETRAALKYLLEAD COMPOUNDS CONTAINING FROM